Efforts to predict corneal ectasia risk secondary to keratoconus or refractive surgery will be greatly facilitated if the measures of corneal biomechanical properties are made available in vivo to improve current diagnoses based on structural (i.e., topographic and tomographic) evaluations alone. For example, mechanical weaknesses (overall or regional) identified in patients? corneas (with or without topographical abnormalities) could alert physicians to closely monitor the condition and potentially initiate interventions to arrest ectatic progression. Clinically, the ability to acquire spatially resolved biomechanical information is still lacking. Many approaches have been proposed, but they often rely on an external force to deform the cornea in order to induce a mechanical response. In addition, most methods do not explicitly address the influence of the intraocular pressure (IOP) on the measured properties. In this project, we aim to build an ultrasound elastographic technique, termed as the ocular pulse elastography (OPE), to characterize the cornea?s response to the cyclic variation of IOP at each cardiac cycle, i.e., the ocular pulse. The baseline IOP and ocular pulse amplitude, which are all measurable in vivo, will be used in combination with the biomechanical measures from OPE to derive the intrinsic tissue biomechanical properties that are independent of the IOP parameters. Our preliminary studies have demonstrated that the OPE technique, based on high frequency ultrasound radiofrequency data analysis, can provide a strain resolution of 0.05% and better, making it possible to reliably measure small in vivo strains induced by an ocular pulse of a few mmHg. In the proposed research, we will (1) validate the OPE technique for mechanical characterization of the cornea; (2) evaluate the sensitivity of OPE in detecting clinically relevant corneal stiffening; (3) define the distribution and variance of OPE-derived corneal stiffness parameters in normal human subjects and their age-associated changes; and (4) test the prediction that corneal biomechanical properties are altered in keratoconus and develop OPE-based biomechanical indices for keratoconus. The first two aims will investigate the relationship between OPE measures and those from traditional mechanical testing, as well as the effects of physiological variables and sensitivity, to build our knowledge of OPE in human eyes under controlled experimental conditions (i.e., in donor eyes) and provide optimal parametric settings and framework for acquiring and interpreting in vivo data. The last two aims of the proposed research will bring the knowledge and technique from the bench to the bedside to acquire in vivo data from normal corneas and those with keratoconus, as the first step of establishing OPE?s clinical use and identifying new, sensitive biomechanical metrics for ectasia risks. The proposed research will address the need for in vivo volumetric biomechanical evaluation of the cornea, leading to a clinical tool for identifying and monitoring biomechanical instability or weakening to aid the diagnosis and treatment of ectatic disease. More broadly, the proposed research will impact the field of ocular biomechanics, by generating in vivo techniques and data to better understand how biomechanics are involved in the health and disease of the eye.